Motor with brush and commutator, and electric apparatus using the same motor

ABSTRACT

An arc length in contact with a commutator of two brushes in a rotational direction of a motor is defined as not more than 5% of an outer rim length or circumference of the commutator, i.e., not more than πA/2O, where A is an outside diameter of the commutator. A number of shorted segments of the commutator, which short is caused by the brush, can be minimized so that reduction in output of the motor can be prevented. As a result, the motor employed in a car product or an electric tool can be downsized and made lighter.

TECHNICAL FIELD

The present invention relates to a motor employed in an electricapparatus such as an automotive product and an electric tool, and anelectric apparatus using the same motor.

BACKGROUND ART

Recently, electric apparatuses such as an automotive product and anelectric tool have been downsized and light-weighted. This market trendentails a power source of these electric apparatuses, i.e., a motormounted to these apparatuses, to be also downsized and light-weighted.

A dc motor having brushes and a commutator is often employed to theseapparatuses. The dc motor comprises the following elements in general:

-   -   a stator producing magnetic field; and    -   a rotor facing the stator via annular space.        As the rotor, an armature including a commutator and an iron        core wound with coils is employed. The armature should be        powered in order to drive the dc motor. For that purpose,        brushes—connected to an outer power source with lead wires—are        brought into contact with the commutator.

The Japanese Patent Application Non-Examined Publication No. H11-341723discloses one of conventional motors of this kind. FIG. 8 shows themotor disclosed, which comprises four magnetic poles, five teeth of anarmature, ten segments of a commutator. The publication also discloses amethod of winding coils as follows, which is illustrated in FIG. 9. Thecoils extended from segments of the same phase are wound on slots(teeth) of the same phase, thereby preventing the output of a motor fromdecreasing.

However, the structure discussed above shorts segments S2 and S3, or S5and S6 with brush B1 or B2 depending on a position where the brushescontact with the segment. As a result, current does not run through somecoils, which are marked with a circle in FIG. 8. In other words, numbersof inactive conductors are produced, thereby reducing the output of themotor, which has been an obstacle to the progress of downsizing andweight reduction of a motor.

SUMMARY OF INVENTION

The present invention addresses the problems discussed above, and aimsto provide a motor downsized and light-weighted without incurringreduction in output. The present invention also aims to provide electricapparatuses downsized and light-weighted, such as car-products andelectric tools, by employing the same motor.

The motor of the present invention comprises the following elements:

-   -   (a) a stator having four magnetic poles;    -   (b) a rotor including:        -   (b-1) a core having five teeth;        -   (b-2) a commutator formed of 10 segments;        -   (b-3) coils wound on the teeth via lead-wires connected to            the segments, and    -   (c) a pair of brushes orthogonally crossing with each other, and        brought into contact with the commutator.

The arc length—contacting with the commutator—of the brushes in therotational direction is defined as not more than 5% of the outer rimlength of the commutator, i.e., not more than π×A/20, where A is anoutside diameter of the commutator.

This structure minimizes a number of shorts between the segments due tothe brushes, thereby preventing a number of active conductors from beingreduced. Further, this structure prevents, as much as possible, thecurrent running through the coils in the same slot from flowing in areverse direction. As a result, a motor accommodating both of downsizingand weight reduction is obtainable without lowering its output.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a cross sectional view of a motor in accordance with afirst exemplary embodiment of the present invention.

FIG. 2 shows a schematic development of a rotor of the motor inaccordance with the first exemplary embodiment of the present invention.

FIG. 3 shows a schematic development of windings of the motor inaccordance with the first exemplary embodiment of the present invention.

FIG. 4 illustrates a method of winding on the motor shown in FIG. 3.

FIG. 5 shows a schematic development of a rotor where contact positionbetween a brush and a commutator of the motor in accordance with thefirst exemplary embodiment of the present invention differs from thatshowed in FIG. 2.

FIG. 6 shows a schematic development of a rotor of a motor, inaccordance with a second exemplary embodiment of the present invention,where a dimensional relation between a brush and a commutator of thepresent invention is applied to a rotor wound by a conventional windingmethod.

FIG. 7 shows a structure of an electric apparatus in accordance with athird exemplary embodiment of the present invention.

FIG. 8 shows a schematic development of a rotor of a conventional motor.

FIG. 9 shows a schematic development of windings of the conventionalmotor shown in FIG. 8.

BEST MODE FOR CARRYING OUT THE INVENTION

Exemplary embodiments of the present invention are described hereinafterwith reference to the accompanying drawings.

First Exemplary Embodiment

FIG. 1 shows a cross sectional view of a motor in accordance with thefirst exemplary embodiment of the present invention. In FIG. 1, motor 31is constructed as follows:

Magnet 37 functioning as a stator is rigidly mounted onto the inner wallof frame 36 of motor 31. Frame 36 houses rotor 35, of which shaft 32extends through the center of core 44 formed of laminatedelectromagnetic-steel plates. Rotor 35 is journaled by bearings 33 and34 at both the ends of shaft 32. Rotor 35 thus faces stator magnet 37via annular space. Rotor 35 is provided with five slots 40 parallel tothe axial line of shaft 32. Five teeth 41 are formed between respectiveslots 40. Windings (coils) are provided on respective teeth 41.Commutator 42 comprising ten segments is rigidly mounted to one end ofrotor 35. Ends of respective coils are coupled to winding connectors 43linked to respective segments. A pair of brushes contact with commutator42, so that commutator 42 slides with respect to the pair of brusheswhen rotor 35 rotates. A pair of brushes 38 and 39 crossing orthogonallywith each other are connected to lead-wires (not shown) through which anouter power source (not shown) powers the coils wound on rotor 35 viacommutator 42. This power feeding generates rotational force betweenteeth 41 of rotor 35 and magnet 37 forming magnetic field, so that rotor35 rotates inside magnet 37 (stator).

The structures of the rotor and the stator are detailed with referenceto FIG. 4, which shows a cross sectional view of the rotor taken alongthe face orthogonal to the section shown in FIG. 1.

In FIG. 4, the inner wall of magnet 37 is magnetized in N-S-N-S at equalintervals in the rim direction, so that magnetic field having fourmagnetic poles is formed. Each of five slots 40, namely 40 a, 40 b, 40c, 40 d and 40 e, is shaped in trapezoid. Between the respective slots,five teeth 41, namely T1, T2, T3, T4 and T5, are formed. Each of teeth41 has two protrusions which cover the adjacent slots on both sides, andthe sectional view of each tooth 41 looks like a T-shaped letter.

Commutator 42 has ten segments, namely segments 1-10 shown in FIG. 4.Each tooth 41 is wound with a coil for driving the motor, and eachcoil-end is connected to each segment.

FIG. 2 shows a schematic development of a rotor of the motor inaccordance with the first exemplary embodiment of the present invention.FIG. 3 shows a schematic development of windings of the motor. FIG. 4illustrates a method of winding coils on the motor shown in FIG. 3.

The motor in accordance with the first embodiment comprises thefollowing elements:

-   -   (a) a stator having four magnetic poles;    -   (b) a rotor including a core having five teeth, a commutator        including ten segments, and coils wound on the teeth via        lead-wires connected to the segments; and    -   (c) a pair of brushes crossing orthogonally with each other, and        contacting with the commutator.

An arc length—contacting with the commutator—of the brush in therotational direction is defined as not more than 5% of the outer rimlength of the commutator, i.e., not more than π×A/20, where A is theoutside diameter of the commutator.

FIG. 2 illustrates that brushes B1, B2 contact with only segments S3, S5respectively. The total length of segments S1-S10 is the outer rimlength of the commutator (π×A) and corresponds to mechanical angle of360°. Both brushes B1 and B2 are disposed such that they crossorthogonally with each other. The space between brushes B1 and B2corresponds to mechanical angle of 90°.

In the conventional case shown in FIG. 8, the positional relationbetween brushes and a rotor (i.e., a commutator) is the same as that inthe first embodiment illustrated in FIG. 2. These two cases are comparedfor finding different results.

In the conventional case shown in FIG. 8, segment S2 is shorted withsegment S3, so that the coil (marked with a circle ◯) starting from S2,winding on tooth T5 and extending to S3 becomes inactive, in otherwords, current does not run through this coil. In same manner, segmentS5 shorts with segment S6, so that the coil (marked with a circle ◯)starting from S5, winding on tooth T1 and extending to S10 becomesinactive, and the coil (marked with a circle ◯) starting from S10,winding on tooth T4 and extending to S1 becomes inactive. The coil(marked with a circle ◯) starting from S1, winding on tooth T4 andextending to S6 becomes also inactive.

In the first embodiment illustrated in FIG. 2 of the present invention,when brush B1 applied with a positive voltage contacts with segment S3,and brush B2 applied with a negative voltage contacts with segment S5,electrical conditions of respective coils are as follows: A firstcurrent runs from B1, through S3, around T5, through S8, around T4,through S9, around T3, through S4, around T2, through S5 and arrives atB2. A second current runs from B1, through S3, around T1, through S2,around T2, through S7, around T3, through S6, around T4, through S1,around T5, through S10, around T1, through S5 and arrives at B2.

In the first and the second current-routes, current runs in the reversedirection in a few coils (marked with ×); however, no inactive coils arefound, which proves that reduction in active conductors of the firstembodiment is smaller than that of the conventional case shown in FIG.8.

FIG. 5 shows a schematic development of the rotor, where another case ofthe first embodiment is illustrated, i.e., a contacting position of thecommutator and the brushes are different from that shown in FIG. 2. InFIG. 5, when brush B1 shorts segment 10 with segment 1, the coil (markedwith a circle ◯) starting from S1, winding on tooth T5 and extending toS10 becomes inactive. However, brush B2 contacts with only segment S3,and thus brush B2 does not short with the adjacent segments. As aresult, a production of inactive coils remains at a lower level than theconventional case.

If a brush's length (arc-length) contacting with the commutator in therim direction is defined not more than 5% (not more than π×A/20, where Ais an outside diameter of the commutator) of the outer rim length of thecommutator, a number of the shorts between the brushes and segmentscaused by a rotor position can be reduced. Because when either one ofthe brushes shorts two segments, the other brush contacts with only onesegment. Thus the reduction in active conductors can be prevented.

The winding method for the motor in accordance with the first embodimentis illustrated in FIG. 3, which shows a schematic development of thewindings of the motor.

In FIG. 3, a first coil starting from first segment S5 is wound on firsttooth T3 closest to S5, and is connected to second segment S6 adjacentto S5. A second coil starting from second segment S6 is wound on secondtooth T2 adjacent to first tooth T3 in the reversal winding direction tothe first coil. Then the second coil is connected to third segment S1corresponding to first segment S5 with respect to third tooth T3adjacent to second tooth T2.

FIG. 4 further details this winding method shown in FIG. 3. In FIG. 4,the mark of × in a circle represents that the winding runs from frontside of the paper to behind the paper (e.g., clockwise viewed from thepaper surface), and the mark of • in a circle represents that thewinding runs from behind the paper to front side of the paper (e.g.,counterclockwise viewed from the paper surface). Segments 1-10 aresimply marked with the corresponding numbers 1-10. A first coil startingfrom first segment S5 (5) is wound in plural turns on first tooth T3closest to segment S5 (5) in the winding. direction marked with thesymbol discussed above. Then the first coil is connected to secondsegment S6 (6) adjacent to segment S5 (5). A second coil starting fromsegment S6 (6) is wound in plural turns on second tooth T2 adjacent totooth T3 in the reversal direction to that of the first coil. Then thesecond coil is connected to third segment S1 (1) corresponding to thefirst segment S5 (5) with respect to third tooth T1 adjacent to toothT2. This winding is applied to all the segments, thereby completing themotor windings.

In FIG. 5, all the segments are provided with the windings discussedabove and shown in FIG. 3, and a dimensional as well as a positionalrelation between the brushes and the commutator is applied. Electricalcondition of respective coils in FIG. 5 is described hereinafter. BrushB1 with a positive voltage contacts with both segments S1 and S10. BrushB2 with a negative voltage contacts with only segment S3. A firstcurrent runs from B1, through S1, around T4, through S6, around T3,through S7, around T2, through S2, around T1, through S3 and arrives atB2. A second current runs from B1, through S10, around T1, through S5,around T2, through S4, around T3, through S9, around T4, through S8,around T5, through S3 and arrives at B2. Current does not run throughthe coil (marked with a circle) wound on tooth T5 and disposed betweenS1 and S10.

As discussed above, when brush B1 shorts S1 with S10, and the otherbrush B2 contacts with only S3 as shown in FIG. 5, a number of inactivecoils (marked with a circle) is less than that in the conventional caseshown in FIG. 8. This fact proves that the reduction in activeconductors is distinctively less than the conventional case.

As shown in FIG. 2 and FIG. 5, the motor in accordance with the firstembodiment can minimize a number of segments shorted by the brush,thereby preventing a number of active conductors from decreasing.Further, the motor can prevent as much as possible the current runningthrough the coils within one slot from running in a reversal direction.As a result, the motor can be downsized and light-weighted substantiallywithout lowering the output.

Second Exemplary Embodiment

FIG. 6 is a schematic development of a rotor in accordance with thesecond exemplary embodiment of the present invention. In this rotor, adimensional relation between a brush and a commutator of the presentinvention is employed; however, the conventional winding method stillremains. FIG. 9 is a schematic development of windings of a conventionalmotor, and this winding method is employed in the second embodiment. InFIG. 9, a coil starting from segment S5 is wound on tooth T2, andcoupled to segment S6 adjacent to segment S5. The coil extending fromsegment S6 is wound on tooth T2, then connected to segment S1. This coilconnection is applied to all the segments of the rotor shown in FIG. 6,and the dimensional relation between the brush and the commutator inaccordance with the second embodiment is applied to this rotor.

In this second embodiment, the conventional winding method shown in FIG.9 can work with the dimensional relation between the brush and thecommutator of the present invention such that even when one brush B1shorts segments S1 to S2, the other brush B2 contacts with only segmentS3 as shown in FIG. 6.

The current routes of respective coils shown in FIG. 6 are as follows:In FIG. 6, brush B1 is applied with a positive voltage, and contactswith both of segments S1 and S10. Brush B2 is applied with a negativevoltage and contacts with only segment S3. A first current starts frombrush B1, and runs through S1, around T4, through S6, around T2, throughS7, around T2, through S2, around T5, through S3 and arrives at brushB2. A second current starts from brush B1, runs through S10, around T1,through S5, around T1, through S4, around T3, through S9, around T3,through S8, around T5, through S3 and arrives at brush B2. No currentruns through the coil (marked with a circle ◯) wound on T4 and disposedbetween S1 and S10.

The second embodiment illustrated in FIG. 6 has less numbers ofin-active coils (marked with a circle ◯), so that the second embodimentis encountered with less reduction of active coils than the conventionalcase illustrated in FIG. 8. As a result, a more efficient motor than aconventional one can be expected by the second embodiment.

When the second embodiment shown in FIG. 6 is compared with the firstembodiment shown in FIG. 5, in the slots circled with ovals, currentruns in a reverse direction through some of the coils, which are foundin greater numbers in the second embodiment than in the firstembodiment. In other words, the first embodiment has less reduction inactive conductors, i.e., the motor of the first embodiment can produce agreater output with a greater number of active conductors if thephysical size is the same as the motor of the second embodiment.Further, at every rotational position of the rotor, a less number ofslots, through which inverse current runs, exist in the winding methodshown in FIG. 3 than that shown in FIG. 9.

Third Exemplary Embodiment

FIG. 7 shows a structure of an electric apparatus in accordance with thethird exemplary embodiment of the present invention. In FIG. 7, theelectric apparatus includes the following elements: (a) housing 51, (b)motor 53 mounted in housing 51; (c) mechanical section 52 driven bymotor 53; and (d) a power supply 54 powered via outside power lines 55.

Motor 53 is driven by power supply 54 via lead wires. Rotating torque istransmitted to mechanical section 52 via an output shaft of motor 53,and mechanical section 52 works to load 56. The motor in accordance withthe embodiments discussed previously is used as motor 53.

To be more specific, the electric apparatus is, e.g., automotiveproducts mounted to an automobile, or an electric tool. A power window,which electrically opens or closes a car window, is one of goodapplications. In this case, housing 51 corresponds to a car body or acar door, power supply 54 corresponds to a battery mounted in the car,mechanical section 52 does to a window opening mechanism, and load 56does to a window. A radiator of the car is another good application. Inthis case, housing 51 corresponds to the car body, power supply 54 doesto the battery mounted to the car, and mechanical section 52 and load 56correspond to a cooling blower.

As the electric tool, an electric driver is a good application. In thiscase, power supply 54 rectifies, smoothes an ac voltage supplied fromthe outside commercial power source, in order to convert the ac voltageto a dc voltage, and powers motor 53. Mechanical section 52 reduces ther.p.m of the output shaft of motor 53 driven by power supply 54, i.e.,increases the torque. Load 56 corresponds to, e.g., screws tightenedinto a board by the electric driver as an output shaft of mechanicalsection 52. Power supply 54 can be a rechargeable battery.

As discussed above, various electric apparatus employ the motor of thepresent invention, and the motor can be substantially downsized andlight-weighted from the conventional motor without reducing its output.Therefore, the electric apparatus employing this motor can be alsosubstantially downsized and light-weighted.

INDUSTRIAL APPLICABILITY

An arc length—contacting with a commutator—of two brushes in arotational direction of a motor is defined as not more than 5% of anouter rim length of the commutator, i.e., not more than π×A/20, where Ais an outside diameter of the commutator. A number of shorted segmentsof the commutator—the short is caused by the brush—is minimized, so thatreduction in output of the motor can be prevented. As a result, themotor employed in a car product or an electric tool can be downsized andlight-weighted.

1. A motor comprising: (a) a stator including four magnetic poles; (b) arotor including: (b-1) a core having five teeth; (b-2) a commutatorhaving 10 segments; (b-3) coils wound on the teeth via connections tothe segments; and (c) a pair of brushes orthogonal to each other andbrought into contact with the commutator, wherein an arc length incontact with the commutator of the brushes in the rotational directionis defined as not more than 5% of an outer circumference of thecommutator.
 2. The motor of claim 1, wherein; a first coil starting froma first segment of the ten segments is wound on a first tooth closest tothe first segment, then coupled to a second segment of the ten segmentsadjacent to the first segment, and a second coil starting from thesecond segment is wound on the second tooth adjacent to the first toothin an opposite direction to the first coil, then coupled to a thirdsegment of a third tooth adjacent to the second tooth, the third segmentcorresponding to the first segment.
 3. An electric apparatus comprising:(a) a housing; (b) a motor mounted to the housing; said motor including:(b-i) a stator including four magnetic poles; (b-2) a rotor including: acore having five teeth; a commutator having 10 segments; coils wound onthe teeth via connections to the segments; (b-3) a pair of brushesorthogonal to each other and brought into contact with the commutator,wherein an arc length in contact with the commutator of the brushes inthe rotational direction is defined as not more than 5% of an outercircumference of the commutator; and (c) a mechanical section driven bysaid motor.
 4. The electric apparatus of claim 3, wherein; a first coilstaring from a first segment of the ten segments of said motor is woundon a first tooth closest to the first segment, then coupled to a secondsegment of the ten segments adjacent to the first segment, and a secondcoil starting from the second segment is wound on the second toothadjacent to the first tooth in an opposite direction to the first coil,then coupled to a third segment of a third tooth adjacent to the secondtooth, the third segment corresponding to the first segment.